Sun Thursday filed a countersuit against rival Network Appliance over patent infringement allegations regarding network storage management software.

Sun filed suit in U.S. District Court in Eastern Texas against the entire NetApp product line, seeking both an injunction and monetary damages.

“It's a responsive action we take not because we want to, but rather because we are forced to,” said Mike Dillon, Sun’s general counsel, in a blog posting Thursday.

The Sun filing is in response to a NetApp suit filed against Sun Sept. 5, also in Texas, alleging Sun’s Zettabyte File System (ZFS) infringed on seven NetApp patents for its Write Anywhere File Layout (WAFL) and RAID technology. NetApp claims that Sun infringed its patents when it released ZFS in 2005 and then released code for it under an open source license this year, as Sun has done with much of its other software.

The NetApp suit followed negotiations going back to 2004 when StorageTek accused NetApp of violating its patents for storage file management software. StorageTek was subsequently acquired in 2005 by Sun, which continued to press the patent infringement allegations against NetApp. Negotiations between the companies eventually led to NetApp’s claim that Sun uses NetApp-patented technology in ZFS.

In a blog posting Wednesday, Sun CEO Jonathan Schwartz acknowledged that open source ZFS is an economic threat to proprietary products such as NetApp’s, but that NetApp’s case has no merit.

“ZFS enables expensive, proprietary storage to be replaced with commodity disks and general purpose servers,” Schwartz wrote. “The economic impact is staggering - and understandably threatening to Net App and other proprietary companies.”

Sun has tried to negotiate with NetApp to avoid litigation, including offering to license open source ZFS to NetApp, he said, but the negotiations failed

“They'd like us to unfree ZFS, to retract it from the free software community, which reflects a common misconception … that you can unfree, free. You cannot,” Schwartz wrote.

Schwartz also reminded Sun customers that Sun indemnifies them from liability in cases where a competitor alleges patent infringement on the part of Sun.

NetApp’s founder and Executive Vice President Dave Hitz, has a blog, too, in which he stated Thursday, “This is exactly the sort of broad but vague threat that gets people so frustrated with patent litigation. Jonathan seems to be arguing that once something has been put into open source, it is beyond the law. I disagree completely!”